The objective of this proposal is to study mechanisms by which the peptide egg laying hormone (ELH) and peptides of the atrial gland (AGP) of Aplysia activate an identifiable neuron in the buccal ganglia of Aplysia. Previous studies have shown that ELH and AGP activate buccal neuron B16, a motoneuron that excites buccal muscle 15. ELH effects on B16 may mediate some of the behavioral changes that occur in association with egg laying, including an inhibition of feeding behavior. Although the functions of AGP are unknown, several of these peptides resemble ELH in structure, and their effects are similar to ELH. Because of the greater amounts of AGP available and the possible similarity in mechanism of action to ELH, experiments with AGP are also proposed. I propose to analyze ionic mechanisms by which ELH and AGP activate identified neuron B16. Preliminary results indicate that this neuron exhibits a voltage dependent conductance decrease in the presence of ELH-containing extracts. The hypothesis is proposed that activation of this neuron at least partly involves decrease of a potassium conductance. The methodology to be used to examine this response is voltage clamp analysis. Specific aims: (1) The effects of ELH and AGP on conductance at various membrane potentials and on the steady-state I-V relationship of the cell body will be studied. (2) The ion dependence of the response will be studied by changing external concentrations of potassium, sodium, calcium, and chloride. (3) The effects of ELH and AGP on specific potassium currents will be studied by observing these currents under specific characterized conditions. Scientific discipline: Basic neuroscience Health relatedness: Mental illness and behavioral disorders rival heart disease and cancer in costs to our nation in morbidity, human suffering and economic loss. Increased knowledge and new conceptions about the role of biological factors in behavioral disorders has come about in recent years through advances in understanding basic mechanisms underlying mental processes; however, much remains to be learned. The proposed project, on hormone mechanisms in the Aplysia nervous system, utilizes a "simple system," which is an historically sound approach to discovering basic mechanisms of broad generalization.